ZF 6 speed in my 5.0 S/C.
Gearbox drained and fresh fluid.

The gearbox will now engage in D or R but after a few seconds it will lose drive. I stop, switch off and wait 5 minutes, and drive is restored for a few seconds and then lost again. Rinse and repeat.

I have checked the fluid level. Gearbox sump temperature 32°C via an IR thermometer and engine running; small trickle.

Sometimes, when returning to P from D or R, I hear a springy gear trying to engage sound.

Anyone any ideas? 2010 5.0 SC Autobiography Overfinch in Bentley Silk White pearlescent, 22" Overfinch wheels with 285/35x22 tyres

Quote:

Sometimes, when returning to P from D or R, I hear a springy gear trying to engage sound.

I had my MY12's output shaft splines re-lubricated at 150K kms. The grease was rather dry but the splines weren't worn at all.

RRPhil wrote:

Quote:

Sometimes, when returning to P from D or R, I hear a springy gear trying to engage sound.

This could be your park lock pawl ratcheting against its gear, which implies that the transmission output shaft is still turning when you are selecting Park. This can only happen (assuming the vehicle is stationary) if there’s some kind of disconnect downstream of the transmission e.g. transfer box, propshafts, final drives or driveshafts.
I would raise the vehicle on its suspension and get someone to look underneath to see if they can see a propshaft or driveshaft turning while you are stationary with D or R selected (obviously, for safety’s sake, they need to be to the side of the vehicle and not underneath it).
Another possibility is that the transmission output shaft spline has failed through fretting corrosion due to lack of lubrication.

Phil

Worn-out fine splines will often grip momentarily, possibly before there's much load on the connection.